Questions for Elevated Bridge

[First Timer]

I bascally started this post for kids to ask quetions and not have to start their own posts.
Anyway I have a question of my own. Does the bridge scoring rely on how much weight your bridge can hold divided by weight? or if it can hold 15 kilos and is as light as possible?

[dudeincolorado]

The scores are the efficiencies of the bridges. So it would be the the weight held (in grams) divided by the weight of the bridge (in grams).

Also be sure to check this out http://www.scioly.org/phpBB3/viewtopic.php?f=16&t=79 its SUPER helpful!

[andrewwski]

Is this dead puppies or kittens or rabbits? I can't keep them straight.

[dudeincolorado]

flies

[captbilly]

You all know what anything divided by zero equals, so what if you could come up with a bridge that weighed zero. Even if it didn't carry any weight it would get a score of infinity. I just can't quite figure out how to get a weight of zero with wood and glue. By the way, though the rules talk about the mass of the bridge the proceedures used don't actually yield a mass but rather a weight. All of the measurements used in bridge, tower, boomilever, etc. use measuring techniques that measure force (weight), not mass. You cannot get the correct mass of an object by measuring against the force of gravity, and eadd the that the fact that the object in question is floating in a fluid (air). SOme of these bridges have densities that are very low, I think the best bridge in 2005 probably had a density of 0.02 g/cc. Air has a density of about 0.0012 so the bridge displaced about 6% of it's mass in air. That means the "mass" of the bridge was actually about 6% higher than the reading on the scale. Of course there also could have been errors due to local variations in gravity, but I think those are generall very small.

[Flavorflav]

You all know what anything divided by zero equals, so what if you could come up with a bridge that weighed zero. Even if it didn't carry any weight it would get a score of infinity. I just can't quite figure out how to get a weight of zero with wood and glue. By the way, though the rules talk about the mass of the bridge the proceedures used don't actually yield a mass but rather a weight. All of the measurements used in bridge, tower, boomilever, etc. use measuring techniques that measure force (weight), not mass. You cannot get the correct mass of an object by measuring against the force of gravity, and eadd the that the fact that the object in question is floating in a fluid (air). SOme of these bridges have densities that are very low, I think the best bridge in 2005 probably had a density of 0.02 g/cc. Air has a density of about 0.0012 so the bridge displaced about 6% of it's mass in air. That means the "mass" of the bridge was actually about 6% higher than the reading on the scale. Of course there also could have been errors due to local variations in gravity, but I think those are generall very small.

Balances find mass, not weight. In some competitions the bridges themselves are massed, although I have never seen a balance used for the weight supported.

[bob3443]

i believe this is + 1 dead kitten

[jander14indoor]

You all know what anything divided by zero equals, so what if you could come up with a bridge that weighed zero. Even if it didn't carry any weight it would get a score of infinity. I just can't quite figure out how to get a weight of zero with wood and glue. By the way, though the rules talk about the mass of the bridge the proceedures used don't actually yield a mass but rather a weight. All of the measurements used in bridge, tower, boomilever, etc. use measuring techniques that measure force (weight), not mass. You cannot get the correct mass of an object by measuring against the force of gravity, and eadd the that the fact that the object in question is floating in a fluid (air). SOme of these bridges have densities that are very low, I think the best bridge in 2005 probably had a density of 0.02 g/cc. Air has a density of about 0.0012 so the bridge displaced about 6% of it's mass in air. That means the "mass" of the bridge was actually about 6% higher than the reading on the scale. Of course there also could have been errors due to local variations in gravity, but I think those are generall very small.

Balances find mass, not weight. In some competitions the bridges themselves are massed, although I have never seen a balance used for the weight supported.

For the displacement issue sited in the first note, balances still have a concern unless the reference mass is near the same density as the weighed object.

For bridge scoring itself, I suspect that while the displacement concern noted by captbilly inflates scores consistently, thus not strongly affecting the placing. I say that because I suspect the density variation of similar mass bridges with similar strength to be fairly small compared to that displacement inflation.

And if you have a competition susceptible to local gravity variations in a gym, you have far bigger noise factors to worry about, humidity, dust, fingerprints...

Jeff Anderson
Livonia, MI

[ichaelm]

First of all:



Second of all, good luck finding wood with the density of air!


EDIT: I think we just got trolled.

[captbilly]

Several years ago a team at Nationals built a bottle rocket that had less then zero weight. It obviously had the highest score (it flew out of sight at several minutes flight time), but was DQed for reasons never fully clear to me. I actually overheard the event coordinators in training for the next year's SO Nationals say that they would not have DQed it. The next year the rules actually included a minimum weight rule (50 grams I believe) to eliminate the possibility of another zero weight rocket. It would certainly be possible to build a bridge with zero weight that was legal (al least legal according to me), although it would not be very strong. It might not even be able to support the loading block. The danger would be that an event coordinator might claim that the bridge "violated the spirit of the competition" which is a rule rarely used but essentially gives the event coordinators the ability to DQ anything that they feel is truly aoutside of what they intended in the rules.

The winners of building events often find creative interpretations of the rules, but there is a line that the event coordinators will not allow you to cross. Sometimes that line is clear, other times it is not so clear.